I believe any person have a facebook account, it means almost people's identity already leaked in the first place.
Having a Facebook account and verifying KYC on a platform isn't the same. Facebook doesn't verify your identity in the first place. Facebook won't know if you are using fake information to create an account. But, Once you create an account on a casino and you have to submit KYC. You cannot submit fake information to verify your account. On top of that, You cannot compare a facebook account with a KYC. Nobody on the internet knows if the account is real or not.
usually at the casino they are not only asked for identity but take a selfie holding a piece of paper with the appropriate date written on it, send bills with the same address name also send video or complicated video calls, this is done to prevent money laundering as well, after all KYC at this casino not the same as facebook even a casino that is much stricter than facebook